The chairman of the leading climate change watchdog was informed that claims about melting Himalayan glaciers were false before the Copenhagen summit, The Times has learnt.

Rajendra Pachauri was told that the Intergovernmental Panel on Climate Change assessment that the glaciers would disappear by 2035 was wrong, but he waited two months to correct it. He failed to act despite learning that the claim had been refuted by several leading glaciologists.

The IPCC’s report underpinned the proposals at Copenhagen for drastic cuts in global emissions.

Dr Pachauri, who played a leading role at the summit, corrected the error last week after coming under media pressure. He told The Times on January 22 that he had only known about the error for a few days. He said: “I became aware of this when it was reported in the media about ten days ago. Before that, it was really not made known. Nobody brought it to my attention. There were statements, but we never looked at this 2035 number.”

Asked whether he had deliberately kept silent about the error to avoid embarrassment at Copenhagen, he said: “That’s ridiculous. It never came to my attention before the Copenhagen summit. It wasn’t in the public sphere.”

However, a prominent science journalist said that he had asked Dr Pachauri about the 2035 error last November. Pallava Bagla, who writes for Science journal, said he had asked Dr Pachauri about the error. He said that Dr Pachauri had replied: “I don’t have anything to add on glaciers.”

The Himalayan glaciers are so thick and at such high altitude that most glaciologists believe they would take several hundred years to melt at the present rate. Some are growing and many show little sign of change.

Dr Pachauri had previously dismissed a report by the Indian Government which said that glaciers might not be melting as much as had been feared. He described the report, which did not mention the 2035 error, as “voodoo science”.

Mr Bagla said he had informed Dr Pachauri that Graham Cogley, a professor at Ontario Trent University and a leading glaciologist, had dismissed the 2035 date as being wrong by at least 300 years. Professor Cogley believed the IPCC had misread the date in a 1996 report which said the glaciers could melt significantly by 2350.

Mr Pallava interviewed Dr Pachauri again this week for Science and asked him why he had decided to overlook the error before the Copenhagen summit. In the taped interview, Mr Pallava asked: “I pointed it out [the error] to you in several e-mails, several discussions, yet you decided to overlook it. Was that so that you did not want to destabilise what was happening in Copenhagen?”

Dr Pachauri replied: “Not at all, not at all. As it happens, we were all terribly preoccupied with a lot of events. We were working round the clock with several things that had to be done in Copenhagen. It was only when the story broke, I think in December, we decided to, well, early this month — as a matter of fact, I can give you the exact dates — early in January that we decided to go into it and we moved very fast.

“And within three or four days, we were able to come up with a clear and a very honest and objective assessment of what had happened. So I think this presumption on your part or on the part of any others is totally wrong. We are certainly never — and I can say this categorically — ever going to do anything other than what is truthful and what upholds the veracity of science.”

Dr Pacharui has also been accused of using the error to win grants worth hundreds of thousands of pounds.

The revelation will cause fresh embarrassment for the The Intergovernmental Panel on Climate Change (IPCC), which had to issue a humiliating apology earlier this month over inaccurate statements about global warming.

The IPCC's remit is to provide an authoritative assessment of scientific evidence on climate change.

In its most recent report, it stated that observed reductions in mountain ice in the Andes, Alps and Africa was being caused by global warming, citing two papers as the source of the information.

However, it can be revealed that one of the sources quoted was a feature article published in a popular magazine for climbers which was based on anecdotal evidence from mountaineers about the changes they were witnessing on the mountainsides around them.

The other was a dissertation written by a geography student, studying for the equivalent of a master's degree, at the University of Berne in Switzerland that quoted interviews with mountain guides in the Alps.

The revelations, uncovered by The Sunday Telegraph, have raised fresh questions about the quality of the information contained in the report, which was published in 2007.

It comes after officials for the panel were forced earlier this month to retract inaccurate claims in the IPCC's report about the melting of Himalayan glaciers.

Sceptics have seized upon the mistakes to cast doubt over the validity of the IPCC and have called for the panel to be disbanded.

This week scientists from around the world leapt to the defence of the IPCC, insisting that despite the errors, which they describe as minor, the majority of the science presented in the IPCC report is sound and its conclusions are unaffected.

But some researchers have expressed exasperation at the IPCC's use of unsubstantiated claims and sources outside of the scientific literature.

Professor Richard Tol, one of the report's authors who is based at the Economic and Social Research Institute in Dublin, Ireland, said: "These are essentially a collection of anecdotes.

"Why did they do this? It is quite astounding. Although there have probably been no policy decisions made on the basis of this, it is illustrative of how sloppy Working Group Two (the panel of experts within the IPCC responsible for drawing up this section of the report) has been.

"There is no way current climbers and mountain guides can give anecdotal evidence back to the 1900s, so what they claim is complete nonsense."

The IPCC report, which is published every six years, is used by government's worldwide to inform policy decisions that affect billions of people.

The claims about disappearing mountain ice were contained within a table entitled "Selected observed effects due to changes in the cryosphere produced by warming".

It states that reductions in mountain ice have been observed from the loss of ice climbs in the Andes, Alps and in Africa between 1900 and 2000.

The report also states that the section is intended to "assess studies that have been published since the TAR (Third Assessment Report) of observed changes and their effects".

But neither the dissertation or the magazine article cited as sources for this information were ever subject to the rigorous scientific review process that research published in scientific journals must undergo.

The magazine article, which was written by Mark Bowen, a climber and author of two books on climate change, appeared in Climbing magazine in 2002. It quoted anecdotal evidence from climbers of retreating glaciers and the loss of ice from climbs since the 1970s.

Mr Bowen said: "I am surprised that they have cited an article from a climbing magazine, but there is no reason why anecdotal evidence from climbers should be disregarded as they are spending a great deal of time in places that other people rarely go and so notice the changes."

The dissertation paper, written by professional mountain guide and climate change campaigner Dario-Andri Schworer while he was studying for a geography degree, quotes observations from interviews with around 80 mountain guides in the Bernina region of the Swiss Alps.

Experts claim that loss of ice climbs are a poor indicator of a reduction in mountain ice as climbers can knock ice down and damage ice falls with their axes and crampons.

The IPCC has faced growing criticism over the sources it used in its last report after it emerged the panel had used unsubstantiated figures on glacial melting in the Himalayas that were contained within a World Wildlife Fund (WWF) report.

It can be revealed that the IPCC report made use of 16 non-peer reviewed WWF reports.

One claim, which stated that coral reefs near mangrove forests contained up to 25 times more fish numbers than those without mangroves nearby, quoted a feature article on the WWF website.

In fact the data contained within the WWF article originated from a paper published in 2004 in the respected journal Nature.

In another example a WWF paper on forest fires was used to illustrate the impact of reduced rainfall in the Amazon rainforest, but the data was from another Nature paper published in 1999.

When The Sunday Telegraph contacted the lead scientists behind the two papers in Nature, they expressed surprise that their research was not cited directly but said the IPCC had accurately represented their work.

The chair of the IPCC Rajendra Pachauri has faced mounting pressure and calls for his resignation amid the growing controversy over the error on glacier melting and use of unreliable sources of information.

A survey of 400 authors and contributors to the IPCC report showed, however, that the majority still support Mr Pachauri and the panel's vice chairs. They also insisted the overall findings of the report are robust despite the minor errors.

But many expressed concern at the use of non-peer reviewed information in the reports and called for a tightening of the guidelines on how information can be used.

The Met Office, which has seven researchers who contributed to the report including Professor Martin Parry who was co-chair of the working group responsible for the part of the report that contained the glacier errors, said: "The IPCC should continue to ensure that its review process is as robust and transparent as possible, that it draws only from the peer-reviewed literature, and that uncertainties in the science and projections are clearly expressed."

Roger Sedjo, a senior research fellow at the US research organisation Resources for the Future who also contributed to the IPCC's latest report, added: "The IPCC is, unfortunately, a highly political organisation with most of the secretariat bordering on climate advocacy.

"It needs to develop a more balanced and indeed scientifically sceptical behaviour pattern. The organisation tend to select the most negative studies ignoring more positive alternatives."

The IPCC failed to respond to questions about the inclusion of unreliable sources in its report but it has insisted over the past week that despite minor errors, the findings of the report are still robust and consistent with the underlying science.